The present invention relates to an ultrathin flexible sheet and a method for manufacturing same. The ultrathin flexible sheet may be suitably used as a cushioning material, sealing material, insulating material, vibration-dampening material, or the like.
Conventional rubber sheets are manufactured by means of calendar extrusion or press-molding (e.g., JP Kokoku 3-29575). In JP Kokoku 3-29575 it has been proposed that kneaded rubber be rolled by a first pair of rolls into a rubber sheet of a prescribed thickness, the rubber sheet be transferred onto a release sheet by a second pair of rolls set to a gap size that is the total of the release sheet thickness and the prescribed rubber thickness, and the resulting article be withdrawn and vulcanized. In JP Kokai 6-190852 it has been proposed that kneaded rubber be calendared to a prescribed thickness, transferred onto a fabric liner, and subsequently withdrawn and vulcanized to manufacture an ultrathin rubber sheet. However, these ultrathin rubber sheets have inadequate strength since they consist solely of the rubber sheet.
Techniques have accordingly been proposed for producing rubber/reinforcing material composites. For example, it is proposed in JP Kokoku 10-138276 that an non-vulcanized rubber composition be applied onto a separator and dried, a reinforcing fabric (non-woven cloth) be laminated on the resulting non-vulcanized rubber composition, and the resulting laminated material be vulcanized under a pressure load to manufacture an ultrathin rubber sheet wherein the ultrathin reinforcing fabric (non-woven cloth) has penetrated, and become integrated with, the rubber layer. An insulating resin film formed by impregnating a stretched porous film material with a silicone rubber solution and subjecting the resulting article to crosslinking polymerization is disclosed in JP Kokai 61-40328. However, these reinforced rubbery articles (e.g., the ultrathin rubber sheet of JP Kokoku 10-138276 and the insulating resin film of JP Kokai 61-40328) have cross-sectional structures of the kind shown in FIG. 1. In other words, not only are the pores 12 of the reinforcing member (e.g., the reinforcing fabric (non-woven cloth) of JP Kokoku 10-138276 and the expanded porous film material of JP Kokai 61-40328) 11 filled with the rubber 21, but the surface 13 of the reinforcing member 11 is covered by a thick rubber layer 22. In JP Kokai 61-40328 in particular, excess silicone rubber is scraped off the surface with a rubber blade after the silicone rubber solution impregnation; nevertheless, a relatively thick layer of silicone rubber will inevitably remain on the surface. As a result, the appearance, surface smoothness, feel, and other attributes are not only degraded, but the risk arises that the rubber portion 22 on the surface will peel off and rubber residues will also remain if the rubber 21, 22 degrades.